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That’s respectable! But yeah, the FHS is something that’s surprisingly hard to find in-depth information about if you don’t already know about it.
I think this page from systemd (or this page from the arch wiki, if you prefer formatting) has a decent description of not only the FHS, but also the more standard user/home structures.
I’m a little confused by that statement. Where should locally installed (non-sudo) applications, such as virtual python envs who are accessed by multiple other not-necessarily-python apps or perhaps baloo, flatpak, etc, store their shared data? I’m rather convinced that giving all users write access to /usr/share is a terrible idea.